how do I convert windows 7 32bit to Windows 7 64bit

I paid ($129.00) for and downloaded an upgrade of Windows 7 32bit from Windows XP (SP3) from the microsoft website, I have since learned that my processor and system can run a 64 bit OS, and I want to know if I can convert to the 64bit version of Windows 7 by downloading.....or do I have to buy a disc with the 64 bit version. I know that I must make a 'clean' install, so I can't simply do an upgrade.....It would be very convenient and cost effective if I could download the 64bit version over the 32bit....thank you for any help you can give me.....Kevin

I said it was the same *serial* for the 2 versions. 32 or 64, they used the same serial number. with the triple pack, I did 2 64 bit installs and 1 32 bit install with the *single* supplied serial number in the case.

Guys, why have you got the idea Khai is asking a question? He does not have a problem, he is just stating the same key works for 32 bit and 64 bit.
He is giving input.

Quotefrom Khai:
" I said it was the same *serial* for the 2 versions. 32 or 64, they used the same serial number. with the triple pack, I did 2 64 bit installs and 1 32 bit install with the *single* supplied serial number in the case."

Rick: " What exactly are you asking ????" Where do you get the idea he is asking anything?
LH: " Khai. You have hijacked this thread. Please could you start a New Topic." Start a topic on what?